(a) Field of the Invention
The present invention relates to a method for producing electrolytic copper foil and an apparatus used for the method, particularly to a method and an apparatus for producing electrolytic copper foil, which is fairly free from internal defects due to uneven formation of crystal nuclei at the beginning of electrodeposition, such as pinholes and curl.
(b) Description of the Related Art
Electrolytic copper foil is commonly produced, as shown in FIG. 1, by mounting in electrolysis tank 1 rotating cylindrical cathode drum 2 and arcuate anode 3 facing each other leaving gap 4, by electrodepositing electrolytic copper foil 6 on the surface of cathode drum 2 by feeding electrolytic solution 5 into gap 4 and applying direct current to electrodeposit electrolytic copper foil 6 on the surface of cathode drum 2, and continuously winding electrolytic copper foil 6.
In the production of electrolytic copper foil, it has been tried to produce pinhole-free copper foil by forming many crystal nuclei densely at the beginning of electrodeposition by using an anode provided apart from the arcuate anode. In the method disclosed in Japanese Patent Application Unexamined Publication No. 9-157883 (1997), a high current anode is provided apart from the anode for electrolysis so that it partially juts out from the overflowing electrolytic solution and faces the surface of the rotating cathode drum where electrodeposition begins, and a current of high current density is applied to the electrolytic solution between the rotating cathode drum and the high current anode, to form many crystal nuclei densely. This method, however, cannot make electrolytic copper foil sufficiently free from pinholes and curl, because the large amount of gas generated by the electrolysis undergoing at the ordinary electrolysis area forms large bubbles as the fluid pressure decreases near the liquid surface, to inhibit uniform supply of the electrolytic solution (copper ions) and uniform formation of the crystal nuclei.
Japanese Patent Application Unexamined Publication No. 10-18076 (1998) discloses preventing the pinhole defects in foil due to the unevenness at the beginning of electrodeposition by providing an auxiliary anode capable of increasing at the beginning of electrodeposition the average current density for the production of foil by more than 60%. The method, due to the large amount of gas generated by the electrolysis undergoing at the ordinary electrodeposition area, also cannot reduce curl and pinholes in electrolytic copper foil sufficiently.
Copper foil used in printed wiring boards or the like has become thinner, causing strict requirements for the prevention of curl and pinholes and demanding techniques of producing electrolytic copper foil freed sufficiently from curl and pinholes.
An object of the present invention is to provide a method of producing electrolytic copper foil whereby the initial formation of the crystal nuclei of electrolytic copper foil can be performed by applying a current of high current density to an auxiliary anode at the beginning of electrodeposition without being affected by the gas generated during the electrolysis at the ordinary electrodeposition area, and the formation of curl and pinholes can be prevented sufficiently. Another object of the present invention is to provide an apparatus to be used for the method.
As the result of study to prevent at the time of the initial formation of crystal nuclei with an auxiliary anode the formation of curl and pinholes due to the gas generated by the electrolysis at the ordinary electrodeposition area, we have found the formation of curl and pinholes in the electrolytic copper foil can be prevented by feeding the electrolytic solution for the initial electrodeposition and the electrolytic solution for the ordinary electrodeposition separately. Based on the finding, we have completed the present invention.
Accordingly, the present invention provides a method of producing electrolytic copper foil, comprising
applying a direct current between a rotating cathode drum having a cathodic drum surface and an anode, which has an arcuate section and faces the cathodic drum surface to define a gap between them, while an electrolytic solution is being fed to the gap to electrodeposit electrolytic copper foil on the cathodic drum surface; and
applying a direct current between the rotating cathode drum and an auxiliary anode, which is mounted together with an electrolytic solution receiver and a flashboard above the anode having an arcuate section, while an electrolytic solution is being fed onto the cathodic drum surface from an electrolytic solution feeder provided near the auxiliary anode and is being discharged through a gap between the cathodic drum surface and an edge of the electrolytic solution receiver while keeping an electrolytic solution holdup between the cathodic drum surface and the auxiliary anode by the electrolytic solution receiver and the flashboard.
The present invention further provides an apparatus for producing an electrolytic copper foil by applying a direct current between a rotating rotary cathode drum having a cathodic drum surface and an anode, which has an arcuate section and faces the cathode drum to define a gap between them, while an electrolytic solution is being fed to the gap to electrodeposit electrolytic copper foil on the cathodic drum surface, comprising
the rotary cathode drum having the cathodic drum surface;
the anode, which has an arcuate section and faces the cathodic drum surface to define a gap therebetween;
a means of feeding the electrolytic solution to the gap between the cathodic drum surface and the anode;
an auxiliary anode facing the cathodic drum surface above the anode having an arcuate section;
an electrolytic solution feeder for feeding an electrolytic solution between the cathodic drum surface and the auxiliary anode; and
an electrolytic solution receiver and a flashboard which are placed above the anode having an arcuate section so as to keep an electrolytic solution holdup between the cathodic drum surface and the auxiliary anode;
a gap being left between the upper end of the anode having an arcuate section and an underside of the electrolytic solution receiver, and a gap being left between the cathodic drum surface and an edge of the electrolytic solution receiver.